crul: HTTP Client

A simple HTTP client, with tools for making HTTP requests,
and mocking HTTP requests. The package is built on R6, and takes
inspiration from Ruby's 'faraday' gem (<https://rubygems.org/gems/faraday>).
The package name is a play on curl, the widely used command line tool
for HTTP, and this package is built on top of the R package 'curl', an
interface to 'libcurl' (<https://curl.haxx.se/libcurl>).